When having students create digital productions like videos the safest way to make sure they avoid any copyright issues is to have them to use their own images and sounds. But if that’s not possible or ideal for your situation, then using Creative Commons media is the next best option. To find Creative Commons licensed media try CC Search.

You can search for images, videos, and audio clips through CC Search. Your search can be refined by usage rights and by media host. CC Search gives you the option to search eight different media hosts for Creative Commons licensed materials. Those eight are: Flickr, Blip.tv, Google Images, Jamendo, Open Clip Art Library, Fotopedia, SpinXpress, and Wikimedia Commons.

Here are some related items that may be of interest to you:
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Six Resources for Learning About Fair Use